Need to remove 20% of water in 25 gallon tank. Help!?

Question

Is this calculation correct to use for a 25 gallon tank?

If you have a 10 gallon aquarium. Calculate 20% of 10 gallons = 0.20 x 10 gallons = 2 gallons. Multiply the 2 gallons times 16 (cups/gallon), to get 2 x 16 = 32 cups. Use a clean measuring cup to remove 32 cups of water from your aquarium. Now mark the level of water in your aquarium with a permanent marking pen or a piece of tape. In the future, drain the water in the aquarium down to the mark and replace it with fresh tap water.

From my calculations, would I be removing 80 cups of water from my fish tank. Is that my 20% of water from my 25 gallon tank.

Answer 1

Yep! 20% of 25 is 5 gallons! Times that by 16 cups and you get 80 cups!

Answer 2

So you calculated you need to remove 32 cups from a 10 gallon tank. Simply use a ratio. The 25 gallon tank is 2.5 times larger (25/10), so you remove 2.5*32, which = 80. 20% is a ratio, 20 parts of 100 parts, or reducing terms, 1 part out of 5. Percentage is simply a ratio of some number to a convenient round number, 100. You could substitute 25 in your sample calculation and figure out the answer of 80 equally as well, but I like the 2.5 times ratio idea better. However, why use cups at all? Why not use a gallon plastic bottle? 20% means removing 1 of every 5 gallons, or 5 gallons total. Using a gallon bottle seems easier the first time and then make a mark, and then later, use a siphon to drain to the mark and refill. The siphon is by far the easiest way to drain water from an aquarium. Just be careful not to suck up the fish!!! When using a siphon, use a tube with a funnel in the tank with mesh netting over the big end of the funnel, which will not allow a fish to get stuck sucked onto the end of the tube.

Answer 3

25 divided by 20% = 25 divided by 1/5

You only need to remove 20% (1/5) of a 25 gallion tank.

25 gallions = 100% (5/5)

subtract 20% (1/5) from 100% (5/5) = 80% (4/5) water left

25 divided by 5 = 5
5 - 4 = 1 x 4 = 4 x 5 = 20

If you take 20% of the water out of a 25 gallon tank you'll have 20 gallons left.

1 US gallon = 8 US pints or 4 US quarts

I am not sure about your calculation though. I found it rather confusing, so I hope this helps a bit. I'd say find something that measures in pints or quarts.

Answer 4

Oh honey, I'd get a clean 5 gallon bucket and drain the tank until that 5 gallon bucket is filled. You may have a hard time lifting the bucket, though, to empty it. Then I'd fill the same 5 gallon bucket up with tap water, treat it with Start Right or some other aquarium water conditioner, and use that to fill the tank. Too heavy again, I know, but can you imagine dipping 80 cups of water. I'd loose count. Make sure that whatever you use to transfer the water is free of soap or other stuff that could affect the fish. Good luck.

Answer 5

Simple way: there are 16 cups in a gallon...
multiply 16 cups times 25 gallons = 400 cups
devide 400 cups by 20% = 80

the way you answered it was the way a teacher would answer it for a student..

Answer 6

ignore the units for now. 20% is the same as .20 and when they say "of" they mean multiply. .20*25=5 but it said to remove that much so you do 25-5=20 left and thats your answer. your removing 5 gallons though.

Answer 7

Yes, but a siphon would work much better than trying to remove 80 cups.

Answer 8

It's not that critical. You can change from 20& to 50% and it won't hurt your system. You can just guess. I've done it for years.

Answer 9

yes.